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Author Topic: Interfacing two independent circuits for a RC car hack project  (Read 1240 times)
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Hello all,

I'm working on a project were a RC car is required to move by itself using an onboard Ardunio (Pro Mini) and proximity sensors. The car should be capable of going into two modes, one where the car will enter autonomous movement when the remote control hasn't been touched for a period of time, and a second mode where the car stops autonomous movement when the remote control is engaged. I have already figured out the pins in the car's controller chip that put out 3V to activate the different movements (forward/backward, left/right). I want the Arduino to have an independent source of power so I need to figure out how to interface them. One way I thought is to break the connections at the IC pins and insert relays between the pins and the PCB that when closed will inform the Arduino about the remote being used and in what direction and another set of relays controlled by the Arduino to open and close the power to the car's motors.

I have a basic knowledge of electronics so I was wondering if the community here could help me with some questions I have:
1. Would standard electromagnetic/mechanical relays be a good solution or can I use optocouplers instead?
2. Are there other kind of switches I could use? The more compact the best due to the limited space inside the car (where I would like to keep all components without having to add extra enclosures).
3. Is there another way of interfacing the two circuits but keep power for the Arduino separated from the car?

Thank you!

Hector
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Hi,
  I've done almost exactly what you are talking about, and it doesn't need relays or optocouplers.  It's just a matter of finding the right place to intercept the signals.  There should be a chip that takes in the RC signal and puts out signals for the motor control circuit. You seem to have identified those.  So all you have to do is intercept the signals between the chip and the motor driver circuit.  Put the chip outputs on arduino pins set for input, and then use some arduino pins in output mode to control the motors.  Your sketch would periodically check to see if there is any input, and if so, switch to "remote" mode.  In remote mode, program the arduino to just pass on the signals.

  The power issue isn't that big a deal, really.  Run your arduino from one battery, and leave the RC car power system as is.  Just be sure that the GROUNDs are tied together, or it won't work. If the chip is really 3v, then you might need a resistor on the output pins to drop the voltage down.

HTH,
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Chris J. Kiick
Robot builder and all around geek.

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Thank you for your reply. What you suggest is exactly what I thought to do first but then I wasn't sure if connecting two different power sources to a common ground would damage the Arduino or the RC car circuits. I'll give your suggestion a try. I'm using 3.3v Arduino Pro Minis so I guess it will be safe to go directly into the RC circuit from the Arduino output.

Hector
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